1. Field of the Invention
The present invention relates to an insulated wire using a resin composition, and more particularly to an insulated wire using a resin composition that are provided with flame retardant property, heat resistance, hydrolysis resistance, and excellent elongation property, in which the resin composition comprises a polyester resin to which various materials are blended (added) or the polyester resin containing the various materials, and the insulated wire comprises a conductor coated with an insulating material comprising the resin composition.
2. Related Art
Conventionally, insulating materials including a polyvinyl chloride (PVC) resin have commonly and widely been used as an electrical insulator. Such insulating materials containing PVC provide advantages of excellent properties in practical use and low cost. However, they have an environmental pollution problem associated with waste disposal because, e.g., they release a gas containing chloride during incineration. Thus, in recent years, there has been a need for an alternative material that can replace PVC. On the other hand, in the transportation industry such as automobiles and trains, there is a growing requirement for energy conservation by reducing the weight of a vehicle body and by saving space for electrical wiring in a vehicle, which in turn causes a demand for lighter and thinner wires.
In order to meet such demand for lighter and thinner wires, however, there is a disadvantage in use of conventional PVC materials that it is impossible to satisfy the required properties such as flame retardant property and abrasion resistance.
On the other hand, the polyester resins that are a type of general-purpose engineering plastic polymers, particularly polybutylene terephthalates (PBTs), are crystalline polymers and excellent in heat resistance, mechanical strength, electrical properties, chemical resistance and moldability. In addition, the polyester resins have properties of low water-absorbing as well as excellent dimensional stability, and readily achieve the flame retardant property. These features allow the polyester resins to be applied to a wide variety of fields such as vehicles, electrical systems, electronics, insulating materials and office automation systems. For example, JP-B-2968584, JP-B-3590057, JP-A-2002-343141 and JP-B-3650474 disclose the polyester resins. Such general-purpose engineering plastic polymers having the above-mentioned features are expected to provide lighter and thinner wires while maintaining flame retardant property and abrasion resistance.
However, since the polyester resins are crystalline polymers, there is a disadvantage in that a crystallization level is changed during the manufacturing process or under particular environment. In particular, the crystallization undergoes by heat treatment at the time of e.g. extrusion molding. Therefore, it is concerned that degradation of a tensile elongation property that is an essential characteristic as the insulating material for an electric wire.
For example, in JP-A-2006-111655 and JP-A-2006-11873, it is proposed that the crystallization is improved by the heat treatment or addition of a crystallization accelerating agent, in order to improve the mechanical strength, high speed molding property and productivity. However, it is concerned that the elongation property may be deteriorated by the acceleration of the crystallization.
Further, in JP-A-2005-213441, it is proposed to suppress the progression of the crystallization by introducing a flexible monomer as a raw material of the polyester resin. However, JP-A-2005-213441 never discloses the elongation property.
In addition, in JP-A-2004-193117, it is proposed to suppress generation of crazing by adding a resin including a functional group that is reactive with a polyester based resin to the polyester resin, thereby suppressing decrease in an insulation breakdown voltage and providing an excellent high temperature insulation property. However, JP-A-2004-193117 never discloses the elongation property of the insulating material for the electric wire under an influence of the heat treatment.